The immobilization of deoxyribonucleic acid (DNA) onto substrates has become an important aspect in the development of DNA-based assay systems as well as for other purposes, including the development of microfabricated arrays for DNA analysis. Substrates for immobilization include the surface of microwell plates, tubes, beads, microscope slides, silicon wafers or membranes.
Hybridization is the method used most routinely to measure biomolecules, e.g., nucleic acids, by base pairing to probes immobilized on a solid support. When combined with amplification techniques such as the polymerase chain reaction (PCR) or ligase chain reaction (LCR), hybridization assays are a powerful tool for diagnosis and research.
A desirable goal for current DNA microarrays is the ability to put an entire species genome on one chip. Also, the ability to place replicates of a smaller set of genes on one chip is desirable. Another sought after goal is that the chips give results that represent the actual population of a specific nucleic acid in a sample.
There is evidence that more hydrophobic surfaces, that are common in the industry, interfere with hybridization process near the surface (Hughes, et. al., Nature Biotechnology 19(4): p 342-347 April, 2001). Assignee's U.S. Pat. No. 6,465,178, demonstrated the utility of slides coated with polyacrylamide copolymers for bioassays in a microarray format. The hydrophilicity of the polyacrylamide backbone provides an environment where surface reactions mimic kinetics and thermodynamics of a solution phase (Dorris, et al., BMC Biotechnology Jun. 11, 2003). However, hydrophilic surfaces can increase spot size. Larger spot size limits the number of spots that can be placed in an array on a surface.
There remains a need for an improved surface that can provide a higher density of spots, and that can retain sufficient hydrophilic character in an aqueous environment and provide solution phase reaction kinetics on the surface.